Since the discovery of high-temperature superconducting materials having superconductivity at a temperature of liquid nitrogen, high-temperature superconducting wires aimed at applications to electric power devices such as cables, current limiters, and magnets have been actively developed. In particular, oxide superconducting thin film wires in which a thin layer made of a rare earth-based oxide superconducting material (hereafter also referred to as an “oxide superconducting layer”) is formed on a substrate have been receiving attention.
Such an oxide superconducting thin film wire is generally produced by forming an oxide superconducting layer made of, for example, an oxide superconducting material represented by REBCO (REBa2Cu3O7-δ: RE refers to “rare earth”) on a wide metal substrate with biaxial orientation and then cutting (slitting) the substrate into a predetermined width (e.g., PTL 1 to PTL 4).
Specifically, first, an oxide layer made of Y2O3 (yttrium oxide), YSZ (yttria stabilized zirconia), CeO2 (cerium dioxide), or the like is formed on a wide metal substrate as a buffer layer by, for example, a sputtering method.
Then, an oxide superconducting layer is formed on the buffer layer by a physical vapor deposition method (PVD method) such as a pulse laser deposition method (PLD method), a sputtering method, or an ion plating method or a chemical vapor deposition method (CVD method) such as a metal organic decomposition method (MOD method).
Then, a silver (Ag) stabilizing layer is formed on the oxide superconducting layer by a sputtering method or the like. Through these processes, a wide oxide superconducting wire is produced.
Then, the wide oxide superconducting wire is subjected to slitting so as to have a predetermined width by using a mechanical slitter, a laser slitter, or the like.
FIG. 4 is a perspective view schematically illustrating an example of a structure of the thus-slit oxide superconducting thin film wire. An oxide superconducting thin film wire 1 includes a metal substrate B, a buffer layer 14, an oxide superconducting layer 15, and a Ag stabilizing layer 16. As illustrated in FIG. 4, a clad substrate including a stainless (SUS) layer 11 serving as a supporting base material, a copper (Cu) layer 12 serving as an orientated layer, and a nickel (Ni) layer 13 serving as an oxidation prevention layer is widely used as the metal substrate B. Herein, the Cu layer 12 and the Ni layer 13 constitute a conductive layer of the metal substrate B.